The present invention relates to a print recording head for impressing an image electrical signal onto a print recording medium, and more particularly, to a print recording head for printing an image by heating a print recording medium itself by the impression of an image electrical signal on the print recording medium and by melting and transferring points of an ink layer provided in the print recording medium.
Heretofore, there have been known the following devices as print recording heads of the above description. Namely, there is known a print recording head 100 on whose tip surface there are arranged linearly recording electrodes 101, 101, . . . with a prescribed spacing, and return electrodes 102, 102, . . . , each of which having a contact area greater than that of the recording electrode 101, on both sides of the recording electrodes 101, 101, . . . , as shown in FIG. 1 (Japanese Unexamined Patent Publication No. 171666/84). As shown in FIG. 2, in this device, the recording electrodes 101, 101, . . . and the return electrodes 102, 102, . . . of the print recording head 100 are brought into contact with a heating resistor layer 104 provided on the surface of a print recording medium 103, a current corresponding to an image electrical signal is passed from a recording electrode 101 via heating resistor layer 104, an electrically conductive layer 105, and the heating resistor layer 104 to a return electrode 102 so as to heat the heating resistor layer 104 at the position corresponding to the recording electrode 101 through which the current is passed. The device has a construction by which the portion of an ink layer 106 provided on the surface of the print recording medium 103 is melted by the generated heat, and printing of an image is carried out by transferring the melted ink onto a transfer paper 107.
Further, a print recording head 109 obtained by laminating recording electrodes 111, 111, . . . made of a patterned metallic layer and an insulating film 112 on a platelike rigid body 110 such as ceramic, as shown in FIG. 3, has been proposed for example, Japanese Unexamined Patent Publication No. 124265/85). As shown in FIG. 4, in this device, a current is passed from a recording electrode 111 to the print recording medium 103 so as to heat the heating resistor layer 104 in the same way as in the above. However, instead of providing a return electrode 102 which returns a current from the conductive layer 105, the current in this device is made to be directly led out from the conductive layer 105 to the outside.
However, in the case of the former device of FIG. 1, there equipped are the recording electrodes 101 and the return electrodes 102 on the contact surface with the print recording medium 103, so that the contact area under pressure of the print recording head 100 is increased and the total contact pressure has to be made high, making it difficult to obtain a uniform pressurized contact. In addition, there is another problem such as an increase in the torque on a driving roll to be provided on the back surface of the transfer paper 107, resulting in a deterioration in the reliability of the printing and recording.
Further, in the latter print recording head 109 of FIG. 3, the end surface of the head has to be brought into plane contact with the print recording medium 103. Accordingly, in order to avoid a straight-forward reduction in the contact factor caused by an oblique contact of the print recording head 109 with the print recording medium 103, it becomes necessary to hold the recording head 109 so as to be always perpendicular to the medium 103, leading to a problem that a highly accurate head holding mechanism has to be provided.
In order to solve the above-mentioned problems, the following devices have been proposed. Namely, the first device 119 is obtained, as shown in FIG. 5, by providing an elastic layer 121 on an electrically insulating substrate 120, and a plurality of recording electrodes 122, 122, . . . in parallel on the elastic layer 121. Here, each of the plurality of recording electrodes 122, 122, . . . is covered with an insulating film 123 except for a portion, and a projected electrode 124 consisting of an electrically conductive material is formed on the portion that is not covered with the insulating film 123 for each of the recording electrodes 122, 122, . . . .
In addition, there is proposed another device obtained by using an elastic metallic plate as the substrate for a print recording head, and disposing a plurality of recording electrodes in parallel on the surface of the metallic plate via an insulating layer.
However, the above-mentioned prior art devices have the following problems. Namely, in the case of the former device of FIG. 5, the elastic layer 121 is provided on the substrate 120, so that even when there is attached a material such as dirt on the print recording medium 103 or the surface of the medium 103 is uneven, a satisfactory contact state can be secured to a certain degree by absorbing the resulting floating of the recording electrodes 122 with the elastic layer 121. However, when there is attached small dirt or the like on the print recording medium 103 of the print recording head 119, part of the electrically insulating substrate 120 will be floated by the presence of dirt or the like from the surface of the print recording medium 103 due to high rigidity of the electrically insulating substrate 120. Then, the print recording head 119 itself is floated because of the sufficiently large rigidity of the electrically insulating substrate 120, causing such problem as missing points in the printed image and the resulting unsatisfactory quality of the image.
Moreover, in the latter case, since the electrically insulating substrate 120 itself possesses elasticity, somewhat large unevenness on the surface of the print recording medium 103 can be absorbed. Now, however, the substrate 120 itself has elasticity, so that the tip of the substrate cannot assure linearity along the longitudinal direction, making it impossible to secure a satisfactory contacting condition with the print recording medium 103 and creating such problem as misalignment in the printed image.
Furthermore, a device with a structure as shown in FIG. 6 which is similar to the printing head as shown in FIG. 5 has also been proposed. FIG. 6(a) shows a lateral cross-section, while FIG. 6(b) stows a longitudinal cross-section of this device. As shown in FIG. 6, on an electrically insulating substrate 120 made of an insulating ceramic, plastic or the like, there are disposed a plurality of recording electrodes 122 formed of an electrically conducting metal (Ni, Cr, Au, Cu, Ta, Ti, Fe, Al, W, Zn, Sn, Pt, Pb, alloys containing these metals, or the like). The electrically conducting substrate 120 and the recording electrodes 122, except for their tips, are covered with an insulating film 123. At these tips there formed protrusions 124 made of an electrically conducting metal (Ni, Cr, Cu or the like) which are connected to the respective recording electrodes 122.
A print recording head 129, in which each electrode body is formed by the recording electrode 122 and the protrusion 124 that are connected to each other, makes a sliding contact with the print recording medium 103 with a tilt of a predetermined angle, as shown in FIG. 7. Here, the print recording medium 103 has a constitution in which a return electrode 105 (Al layer) and an ink layer 106 are laminated on a film like electrically conductive heating resistor layer 104. With the return electrode 105 being grounded, a prescribed amount of current is passed via the recording electrode 122 and the protrusion 124 which correspond to a print dot by causing the protrusion 124 which forms a part of the print recording head 129 to make a sliding contact with the surface of the heating resistor layer 104. Then, the current flows spotwise from the sliding contact portion of the protrusion 124 through the heating resistor layer 104 to the return electrode 105. In this current flow, the portion of the heating resistor layer 104 through which the current is passed is heated up, and ink 106a at the position corresponding to the heated site is transferred to the recording sheet.
However, the life of the prior art print recording head 129 of the above kind is not sufficiently long. This is because the electrode body which ordinarily constructed with a metallic material is operated in a state where it makes a sliding contact with the heating resistor layer 104, so that the surface of the sliding contact is worn out relatively soon, and its exposed surface is oxidized due to heating at the time of ink transfer.